Process of exfoliating marine shell platelets



Patented May 22, 1951 PROCESS OF EXFOLIATING MARINE SHELL PLATELETSJoseph H. Hooton, Englewood, N. J assignor to Richelieu Corporation, NewYork, N. Y., a corporation of New York No Drawing. Application April 9,1949, Serial No. 86,599

Thisinvention relates to a new and novel process of separatingiridescent crystal platelets from marine and fresh water shells.

The beautiful appearance of the nacre or mother-of-pearl materialcontained in fresh Water or marine shells such as the abalone shells,snail shells, pearl oyster shells and other mussel shells is well knownand it has often been tried to separate the crystals or platelets insuch a condition that they could be employed for imparting a decorativeeffect to other materials.

The decorative portion of these shells is made up of platelets orlamellae of calcium carbonate crystal particles held together by aproteinaceous substance called conchiolin. crystals by a delamination orexfoliation process all of the protein binder must not be removed oraltered because it is apparently the thin coating of this material onthe calcium carbonate crystals which gives such crystals theiriridescence and shiny appearance. The lamella can be separated by heatalone but this process destroys or changes the conchiolin or proteinbinder so that only dull, white or gray crystals are ob tained.

These shell crystals have attracted the attention of man inventors andmany attempts have been made to separate the plate like crystals fromeach other and from the remainder of the shell. For example, U. S.Patent No. 1,570,183 discloses that the laminae or flakes may beseparated by heating the shells. Heat however destroys a considerableportion if not all of the luster of the crystal particles. U. S. PatentNo. 1,812,885 discloses a process of exfoliating the shells by heatingin the presence of water at relatively high temperature and pressures.U. S. Patent No. 2,172,369 discloses another process of producing suchcrystals which involves heating the shells in the presence of a mildaqueous alkaline solution. The heat required according to this latterpatent is less than that required in the other two patents butnevertheless theshells are eventually subjected to the alkaline solutionat a temperature of 100 C. This patent also discloses but does not claima process of exfoliation at 25 in ammonia solutions but the timerequired is excessively long. There is evidence to indicate that theiridescent appearance of the crystals in a shell is at least partly dueto a thin coating of proteinaceous material on the surface of thecrystal particle. Any considerable amount of heat is also known to causecoagulation or denaturation of proteins. If the crystal particles couldbe separated by'processes involving not In separating the 5 Claims. (Cl.252378) heating of the crystals there would be less likelihood ofdamaging the surface coating of the crystals and the resultant productsshould have increased luster and sparkle.

An object of this invention therefore is to provide a process ofseparating the crystal plate:- lets from shell particles Withoutsubjecting the crystal platelets to temperatures of boiling water or anytemperature suificiently high to cause coagulation or denaturation ofproteins.

Another object of this invention therefore is to provide a process forseparating decorative, iridescent, silvery and sparkling crystals frommarine and fresh water shells.

Another object of the invention is to provide a process of separatingthe crystal platelets of marine and fresh water shells in substantiallythe same state as they appear in the shells.

Another object of the invention is to provide a method of exfoliatingshell material Without destroying the proteinaceous coating on thecalcium carbonate particles of the shells.

Another object of the invention is to provide a method for producingsilvery bleached crystal platelets from shells, which platelets retaintheir natural sparkle and iridescence.

These objects and others ancillary thereto are obtained by exfoliatingthe shells or shell fragments by a mild chemical treatment with anaqueous solution containing a mild alkaline bufier reagent such as analkali phosphate. Preferably before or during the treatment the shellsare subjected to a mechanical or a chemical process to remove the backsor other portions thereof which might produce discolored particles andit is also desirable to grind, cut orcrush the shells to fragments ofconvenient size, for example, to a size of 1.4" to 2 inches on a side.

Prior to and/or during exfoliating the shell particles are preferablytreated with a bleaching agent to produce a product with more of asilvery aspect. In the last stages of the exfoliating process,especially, the process is carried out Without subjecting the particlesto high temperatures and preferably without any extraneous heat. 1 5

The phosphates which may be employed in the exfoliation process includethe diand trisodium phosphate (NazHPOr) and (Nazi-"04) sodiumpyrophosphate (NarPzOv), -sodium tripolyphosphate' (Na5PaOm), the sodiummetaphosphates, (NaPOa), sodium monothiotetra phosphate (NasP4012S)sodium trithiotetraphosphate (NasPrOmSa) sodium tetraphosphate(Na6P4013) mixtures of such phosphates, and -the .agents isunpredictable.

3 corresponding potassium, ammonium and lithium compounds.

Alkaline reagents such as ammonium, sodium or potassium carbonates areadded to the phosphate solutions to produce a solution which has a pH of10-13. It is also possible to employ a dilute solution of the alkalihydroxides, without additional phosphates, in the early stages of theexfoliation process but the final exfoliation step should be conductedwithout heat and in the absence of strong alkalies. The alkali solutionshould be of less than normal concentration and the product should bethoroughly washed after the treatment. It is preferred to conduct theexfoliation treatment with alkaline solutions at room temperatures butit is possible to heat the alkaline exfoliating solutions to as high as70 C. Without destroying too much of the luster and silvery appearance.The treatment with chlorine water restores the silvery luster and insome cases even increases the silvery appearance to .a greater degreethan that present in the original shells.

This improved sparkle and silvery luster produced by treatment with themild oxidizing For such treatments aqueous solutions of chlorine,oxygen, hydrogen peroxide, sodium peroxide and sodium hypochlorite havebeen found suitable. Bleaching agents, such as potassium permanganate,which impart a color to aqueous solutions do not improve the luster ofthe product.

It is sometimes desirable to conduct the exfoliation treatment with thealkaline solutions in several stages the most drastic treatment being Iand color is obtained in the final product.

The novel features characteristic of this invention are set forth withparticularity in the appended claims. The invention itself, however,both as to its organization and its method of operation, together withadditional objects and advantages thereof, will best be understood fromthefollowing description of specific embodiments when read inconnection. with the following examples:

Example 1 'Ihe'shells known commercially as Kapiz shells (the scientificname is Placuna Placenta Linn) having the unsightly backs removed (as bygrinding) are broken into fragments averaging about /;to 1 square inchin size.

One hundred pounds of these fragments are then placed in a vessel andcovered with a solution of 12 pounds of trisodium phosphate in190'pounds of water to which are added 5 pounds of a mixture of thesodium tetraphosphate with the sodium mono and trithiotetra phosphates.

This mixture of shells and liquor is allowed to stand at roomtemperature for 48 hours during which time the crystals are exfoliated.

The solution is poured oil" and the separated crystals are washed withcold water until the chemicals from the previous treatment areeliminated. The flat platelets or crystals which separate are about to/4 on a side and have a sparklingand iridescent appearance. Thesecrystals are then dried in a current of air which, while the crystalsare still damp, may have a tempera ture as high as 250 F.

Example 2 Kapiz shells are cleaned and crushed or ground to a size of toon a side. The broken shell is treated in 3% hydrochloric acid to removethe discolored porous backs and then washed with ordinary water toremove the remaining acid and soluble salts resulting from the acidtreatment.

These shell particles are then placed in a chlorine solution made up asfollows:

Water, 48 gallons 15% solution of gaseous chlorine, 9 gallons Shellparticles, pounds The shell particles are soaked in this solution atroom temperature for 2 hours. Then the solution is poured off and theshells are washed with 50 gallons of cold water.

To the shell particles 'there is now added 24 gallons of water, 23pounds of trisodium phosphate, 1 pound of ammonium chloride and 2 poundsof sodium carbonate and 50 cc. of a fluorescene dye solution (made bydissolving 4 g. of fluorescene dye in 400 cc. of water). The shell massis allowed to remain in this solution for 20. hours at room temperatureand then the liquor is poured off and the resulting exfoliated crystalsare washed until the powdered fragments and chemicals are removed.Thereafter the crystals are dried at 200 F. The crystals so producedhave a silvery opaque background with a sparkling iridescent coating.

Example 3 '75 pounds of clean Kapiz shells are crushed or ground toparticles having dimensions of between and The ground shell particles.aresubmerged in 17 /2 gallons of water to which 750 g. of sodiumhydroxide is added to produce a solution having a normality of N/ 3 toN/ l. The shells are allowed to remain in this solution for 1 hour andare stirred several times during that hour. The solution is then removedand the particles are washed three times with water. The crystals of theshell particles are partially exfoliated at this point in the process.

The shell particles retain a considerable amount of the wash water andto the water containing shell particles 3 gallons of a 15% aqueoussolution of gaseous chlorine and enough water to raise the level of thesolution to the original amount of 17 gallons are added (about 9 gallonsof water are usually required). The shell particles are permitted tosoak in this solution for 1 hour and then the solution is drained offand the particles are washed three times with cold water.

To the shell particles and entrained wash water, 5 gallons of a solutioncontaining /2 lb. of sodium carbonate and 12 lbs. of trisodium phosphateare added. The shell particles are left in this solution, withoccasional gentle stirring for 15 hours. This completes the exfoliationof the crystals. The resultant crystals are washed with cold water anddried at 200 F.

Ezrample 4 Occasionally it is necessary to treat shells which are verydirty and the following procedure is recommended. The shells are groundas to a particle size the dimensions of which are to The crushed orground shell particles are placed in a cylindrically shaped sieve theopenings of which are slightly less than the smallest dimension of theparticles. This sieve containing the particles is rotated in a hotliquid bath containing a detergent. For example, a bath containing 13lbs. of trisodium phosphate and 1 lb. of soap powder at 200 F. issatisfactory. The shell particles are rotated in the sieve until cleanedwhich may take as long as 1-2 hours depending on the condition of theshells. This treatment, in addition to washing out the dirt and smallshell fragments and dust, starts the exfoliation process. The product isfinally rinsed with water.

The shell particles (containing entrained water) are then treated with8% gallons of a solution containing 13 lbs. of trisodium phosphate, lb.of sodium carbonate and 165 fluid oz. of a 30% hydrogen peroxidesolution are added to the treating liquor. This treatment is continuedfor 2 hours.

The resultant shell particles are then washed and submerged in Water towhich hydrochloric acid is added in suflicient amount to make about a 3%solution. This treatment is continued for 20 minutes and the product isimmediately washed with at least 3 rinses of Water. This treatmentremoves the backs of the shells and the surface layers of crystals whichmight have been damaged by the hot washing treatment.

This product which is almost completely exfoliated is further treatedfor about one hour with an aqueous solution containing about 3 /2% ofchlorine gas to further bring out the silvery luster of the crystals.

The crystals are washed and the exfoliation is completed in an aqueoussolution containing 12% of trisodium phosphate and /2% of sodiumcarbonate. This final mix is gently stirred occasionally to facilitateseparation of the crystals. The resultant crystals are washed, dried,sieved to remove small particles and packed.

The crystals produced by the above processes are substantially flat twodimensional crystals having one narrow dimension of about 1% to and onelong dimension of about /8 to A.". The crystals have a silveryiridescent luster which is even superior to that of the crystals whenseen in the original shell. When fluorescene dye is included in thetreating solution the crystals also have a pinkish case or a bluish orgreenish case when umbelliferone is included in the treating liquid.

I claim:

1. A process of obtaining silvery, iridescent crystal platelets fromfresh water and marine shells comprising the steps of dividing theshells into small fragments, treating the shell fragments with anaqueous alkaline solution containing an alkali phosphate compound andhaving a pH of 10-13 at temperatures of less than 70 C. to exfoliate thecrystal platelets.

2. A process of obtaining silvery, iridescent crystal platelets fromfresh water and marine shells comprising the steps of dividing theshells into small fragments, treating the shell fragment with an aqueousalkaline solution containing an alkali phosphate compound and having apH of 10-13 at temperatures of less than C. discontinuing the treatmentbefore the crystal platelets are completely exfoliated, treating thepartially exfoliated crystal platelets with an aqueous solutionconsisting essentially of water and an oxidizing gas, and completing theexfoliation by treatment with an aqueous alkaline solution containing analkali phosphate compound and having a pH of 10-13 at temperatures or"less than 70 C.

3. A process of obtaining silvery, iridescent crystal platelets fromfresh water and marine shells comprising the steps of dividing theshells into small fragments, removing the back portions of the shells,treating the shell fragments with an aqueous alkaline solutioncontaining an alkali phosphate compound and having a pH of 10-13 at roomtemperature discontinuing the treatment before the crystal platelets arecompletely exfoliated, treating the partially exfoliated crystalplatelets with a solution containing an oxidizing gas, washing theresultant mass, and completing the exfoliation by treatment with anaqueous alkaline solution containing a fluorescene dye and an alkaliphosphate compound and having a pH of 10-13 at room temperature.

4. A process of obtaining silvery, iridescent crystal platelets fromfresh Water and marine shells comprising the steps of dividing theshells into small fragments, treating the shell fragments at roomtemperature with an alkali hydroxide solution of less than normalstrength to start exfoliation of the crystal platelets, Washing theresultant mass, treating the partially exfoliated crystal platelets withan aqueous solution consisting essentially of water and an oxidizinggas, washing the resultant mass, and completing the exfoliation bytreatment with an aqueous alkaline solution containing an alkaliphosphate compound and having a pH of 10-13 at temperatures of less than70 C.

5. A process of obtaining silvery, iridescent crystal platelets fromfresh water and marine shells comprising the steps of dividing theshells into small fragments, treating the shell fragments with anaqueous alkaline solution containing a fluorescent dye, an alkaliphosphate compound and having a pH of 10-13 at temperatures of less than70 C. to exfoliate the crystal platelets.

JOSEPH I-I. HOOTON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,570,183 Rauschenberg Jan. 19,1926 2,172,369 Eolis Sept. 12, 1939

1. A PROCESS OF OBTAINING SILVERY, IRIDESCENT CRYSTAL PLATELETS FROMFRESH WATER AND MARINE SHELLS COMPRISING THE STEPS DIVIDING THE SHELLSINTO SMALL FRAGMENTS, TREATING THE SHELL FRAGMENTS WITH AN AQUEOUSALKALINE SOLUTION CONTAINING AN ALKALI PHOSPHATE COMPOUND AND HAVING APH OF 10-13 AT TEMPERATURE OF LESS THAN 70* C. TO EXFOLIATE THE CRYSTALPLATELETS.